Abstract
Cotton-tipped applicator swabs are used as a collection device for many biological samples and its complete elution is a desired step for clinical and forensic diagnostics. Swabs are used to collect infectious body fluids, where the concentration of pathogens can range from 1 × 104 CFU/mL (colony forming units/mL) in respiratory-tract infections and 1 × 105 in urinary-tract infections, to up to 1 × 109 CFU/mL in salivary samples. These samples are then eluted and lysed, prior to DNA (De-oxy Ribonucleic Acid) analysis. The recovery of micro-organisms from a matrix of swab fibres depends on the nature of the body fluid, the type of the swab fibres, and the process of elution. Various methods to elute samples from swab include chemical digestion of fibres (~20% recovery), centrifugation (~58% recovery), piezoelectric vibration, or pressurized fluid-flow (~60% recovery). This study reports a magnetically-actuated physical impingement method for elution and recovery of artificial sputum samples from cotton fibres. A device has been fabricated to induce a rotating magnetic field on smaller magnetic particles in a vial that strikes the swab within a confined gap. Elution from the swab in this device was characterized using 2% Methyl cellulose in deionised water, loaded with fluorescent-tagged polystyrene beads and E. coli at various concentrations. The recovery efficiency was found to increase with both rotational speed and elution time, but plateaus after 400 RPM (Revolutions per minute) and 120 s, respectively. At a higher concentration of polystyrene beads (5 × 108 particles/mL), a maximum recovery of ~85% was achieved. With lower concentration, (1 × 105 particles/mL) the maximum efficiency (~92.8%) was found to be almost twice of passive elution (46.7%). In the case of E. coli, the corresponding recovery efficiency at 3.35 × 105 CFU/mL is 90.4% at 500 RPM and 120 s. This elution method is expected to have a wide applicability in clinical diagnostics.
Highlights
Sampling and elution are the very first steps in the preparation of biochemical assays, which are used in the clinical testing or analysis of environmental samples
In order to demonstrate the increase in elution from the swab due to impingement of the magnetic particles, experiments were performed in settings with and without magnetic agitation, using swabs that were dipped in artificial sputum samples containing polystyrene beads
Unlike the no agitation case, where the time constant that is associated with the dissolution process is long and only the sample at the surface layers of the swab get effectively eluted, under magnetic impingement, is the surface elution rapid, but the impingement imparts forces to actively mix the sputum sample between the deeper layers of the swab and the surface layers that have absorbed the elution buffer from outside
Summary
Sampling and elution are the very first steps in the preparation of biochemical assays, which are used in the clinical testing or analysis of environmental samples. Swabs are widely used to collect biological samples, such as saliva, nasal sputum, semen, blood, or urine from the human body. They are made of cotton, rayon, polyurethane foam, or polyester, and are available in a spun or flocked tipped format. Cotton based collection methods are the most widely used sample collection techniques with salivary or sputum based immunoassays because of its easy availability, low cost and high absorbance. Apart from biological samples, swabbing techniques are used for DNA analysis of touched evidence [1], recovery of spores from environmental surfaces [2,3], or the removal of dried blood stains [4]. Depending on the field of application, the type of swab used could vary
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